Developing In-Vitro Models of A Toxicity: Complementary Yeast and Human Stem Cell approaches over 5 million americans have been diagnosed with Alzheimer's disease (AD). This patient population is expected to increase in the coming years as the number of elderly individuals grows. In turn, this growing patient population confers a need for increased funding to treat and care for affected individuals. Currently, no available treatments can add five or more years of symptom-free life to an individual with AD. One major obstacle to the development of novel therapeutic compounds has been the inability to obtain the neural tissue types impacted by AD for study. To address this issue, many research groups have developed model in vitro systems which facilitate the study of the disease course. Our group has previously developed a Saccharomyces cerevisiae model of amyloid beta 42 (A42) toxicity. A42 is commonly thought to be the culprit which underlies the neuronal apoptosis which occurs during AD progression. This yeast model has been used in genetic screens and uncovered therapeutic targets which modulate A42 toxicity. AIM 1 of the current proposal is to further characterize these genetic modifiers through loss-of-function studies. While the tractability of yeast provides a powerful model for identifying novel therapeutic targets these targets must be confirmed in clinically relevant models before therapeutic testing can be contemplated. Recently, human embryonic stem (hES) cell derived neurons have proven to recapitulate important aspects of neurodegenerative disorders in an in vitro setting. Therefore, in AIM 2 I propose to establish a complimentary human stem cell model of A42 toxicity. Furthermore, in AIM 3 I will use the established human stem cell model to confirm our previous findings in yeast in clinically relevant cell types and probe the influence of ApoE genotype on A42 toxicity. Together, these studies will delve deeper into possible therapeutic targets for A42 toxicity which could lead to efficacious compounds in future small molecule screens.